The present invention relates to data processing systems employing shared resources; more particularly, to an enhanced control of said shared resources for enabling more flexible data-processing systems operations while ensuring data integrity.
In data processing systems, many peripheral equipments are shared between a plurality of hosts (central processing units). Even if a single unit of peripheral equipment is attached to but one host, a plurality of independent computer processes performed within that host on a multi-processing basis may desire to share the peripheral equipment. Further, in multi-host data processing sites, a single peripheral device may be shared through a single host by a plurality of hosts connected to the single host. Examples of such shared peripheral equipment are of the peripheral data storage apparatus such as magnetic storage tape apparatus, magnetic disk apparatus, optical storage apparatus of all types, printers of all types, communication equipment including concentrators, modems, terminals, and all other sorts of equipment that can be connected to and used in connection with a data processing system.
In a plural-host data-processing system, the host, in addition to communicating with peripheral equipment, also employ what is termed in this application "lateral communications" between the hosts. This lateral communication includes direct host-to-host signal transfers. Such networking in a multi-host data processing system facilitates multi-pathing and enables better control and efficiency of a multi-processing multi-host system that can be interactive to various degrees. When such systems employ shared resources, the domination of a shared resource, such as a peripheral equipment, by one host to the exclusion of other hosts or by one process to the exclusion of other processes can cause degradation of overall data-processing system's performance. Such degradation can be caused by error conditions as well as a process or host that in its normal day-to-day operations tends to dominate a given peripheral equipment. Such limited access results in access "contention". In such a multi-unit data processing system, resolution of contention in an efficient manner can improve data processing performance. Lateral communications can facilitate error condition analysis for minimizing throughput degradation, particularly as enhanced by the present invention.
Accordingly, peripheral equipment that are shared resources, as well as other forms of shared resources, should provide for more efficient contention resolution and error analyzation such that utilization of shared resources can be maximized by its connected data processing system. Since multi-pathing can raise questions of data integrity, such shared resource should enable an additional check on the operation of such shared resource for giving an added confidence level to data integrity of the data handled by the shared resource, particularly when that shared resource is storage apparatus.